Printing devices, such as laser printers, use a printing composition (e.g., ink or toner) to print text, graphics, images and the like onto a media substrate. Laser printing processes utilizing such devices employ static electricity to secure images to the substrate. A photoreceptor or drum in the printing device, which is formed of a highly photoconductive material, is given a positive charge by a wire having an electrical current running therethrough. Once the surface of the drum is charged, a laser beam shines across the charged photoreceptor surface to discharge certain regions thereof. In this way, the desired image is formed, temporarily, on the surface of the photoreceptor. Such image is often referred to as an “electrostatic image”. Once the electrostatic image is formed, the photoreceptor is coated with positively charged toner which clings to the negative discharged regions of the drum. With the toner pattern affixed, the drum rolls over a media substrate having a negative charge which is moving along on a belt below the drum at substantially the same speed at which the drum is rotating. The negative charge of the media substrate is stronger than that of the electrostatic image and, thus, the media substrate pulls the toner away from the photoreceptor and an exact duplicate of the electrostatic image is formed on the substrate surface.
Once all of the toner has been passed to the media substrate, it is directed through a fusing station, which is typically a pair of heated rollers. As the substrate passes through the rollers, the toner melts, fusing with the fibers in the media substrate. The paper is then passed into the printer output tray and printing of the desired image is complete.
The quality of the image formed on a media substrate as just described depends on a number of factors, including the surface characteristics of the substrate itself. Various media substrates may be used in the laser printing process including, but not limited to, letter quality paper, envelopes, photographic print stock, transparencies and the like. Some media substrates have a finish on the surface thereof which is glossy (e.g., transparencies and photographic print stock) while other substrates have a finish which is matte (e.g., envelopes and letter quality paper). The terms “glossy” and “matte” refer generally to the amount of light which is reflected from the surface of the substrate when it is illuminated by a light source, with glossy media substrates reflecting more light than matte media substrates. In order to achieve optimal printed output, whether a media substrate is glossy or matte, and the level of gloss reflected therefrom, should be determined and taken into account during printing and the printing parameters set accordingly.
The gloss level of a media substrate on which printing is desired may be accounted for in the printing process by a user manually adjusting the printing device in accordance with the determined gloss level. For instance, a user may be presented with options to input whether the media is glossy or matte, or may be prompted to select the particular media substrate type from a pre-established list of media substrate types for which the level of gloss is defined and stored by a printer driver or controller. This method may be undesirable, however, in that users are often unable to differentiate between glossy and matte substrate finishes and/or may be unaware of the type of media substrate being used. If the media characteristics are incorrectly input, an optimal printed output may not be achieved.
Several methods have been proposed by which the above-stated drawbacks to user intervention in the printing process may be alleviated. For instance, a method has been disclosed for differentiating between glossy-finish and matte-finish print media by detecting whether a reflected light signal is polarized or unpolarized. Sheets of print media having a matte-finish reflect unpolarized light signals and sheets of print media having a glossy-finish reflect polarized light signals. Thereafter, the media detector communicates a signal to a controller coupled to the media detector and the controller adjusts the printing device for printing on glossy-finish print media or matte-finish print media based on the signal received from the media detector.
Another method for determining gloss level of a media substrate with little or no user intervention is a method for determining, based upon gloss level, the media type of a sheet of print media prior to printing. In the method, a reference surface is illuminated and the spectral reflection intensity is measured by a sensor and assigned a first value. Subsequently, a media sheet is moved onto the reference surface, the sheet is illuminated and the spectral reflection intensity is measured by a sensor and assigned a second value. The ratio of the first spectral reflection intensity to the second spectral reflection intensity is compared to a threshold value selected from a set of predetermined threshold values to identify the media by gloss level.
In another method, a system of classifying the type of media to be printed upon in an inkjet printing mechanism is provided. A portion of a print media is scanned several times to generate a collection of reflectance values which are then averaged to determine a classification value. The classification value is then analyzed through comparison with known values for different types of media to classify the print media as one of the pre-defined types.
In order to achieve a substantially optimal printed output, the toner fused to the media substrate should have substantially the same gloss level as the unprinted surface of the media substrate itself. Thus, once the media substrate gloss level is determined and input into, or otherwise communicated to, the printer driver or controller, the printing parameters may be adjusted in an effort to match the gloss level of the toner to that of the media substrate. Commonly adjusted printing parameters include the temperature of the fuser rollers and the fuser pressure. If the gloss level of the media substrate is high, the temperature of the fuser rollers may be increased and/or the fuser pressure increased to produce a glossy image thereon. Alternatively, if the gloss level of the media substrate is low, the temperature of the fuser rollers may be decreased and/or the fuser pressure decreased to produce a matte image. Exactly how high the temperature or how the pressure of the rollers is to be adjusted is generally predetermined and stored in the printer controller with certain parameters corresponding to certain media types; the media types also being predetermined and stored as discussed with the prior art methods, above.
One method for achieving a pre-selected gloss level by choosing the appropriate fuser temperature is, the method of establishing a gloss value for a pre-defined gloss and, subsequently, selecting a fusing temperature and fusing period in accordance with the gloss value. The fusing temperature and/or rotation speed of at least one fuser roller is then controlled within the defined temperature and fusing period ranges. Stated differently, a user selects the desired gloss level from a pre-defined set of gloss levels, inputs the desired level into a controller and a microprocessor subsequently sets the fusing temperature and period parameters to achieve the desired gloss level. The microprocessor may take into account other factors, such as the paper thickness, the toner type, the paper weight, the humidity and the rigidity of the paper, in establishing the parameter selections.
In each of the above described methods, the gloss level of the desired media substrate is determined and subsequently compared to a predetermined and predefined list of media substrates. The user or the printer controller determines which substrate type gloss level from the predefined list most closely approximates the gloss level of the substrate on which printing is desired and adjusts the printing parameters in accordance with parameters predetermined and stored as associated with the predefined substrate. These methods still may not achieve optimal print output as the media selections are based on a finite number of predetermined thresholds. Thus, if the media on which printing is desired is not among those having printing parameters predefined and stored in the printer controller, an approximation must still be made and the parameters set to maximize printing for that media substrate having a gloss level which most closely approximates that of the substrate to be printed.
Accordingly, a method and device for optimizing print output by accurately matching the gloss level of printed and unprinted regions of a media substrate would be advantageous. Further, a method and device which permits customization of printing parameters to any desired media substrate would be desirable.